Preparation of amines and aminonitriles

ABSTRACT

A process for the coproduction of 6-aminocapronitrile (ACN) and hexamethylenediamine (HMD) by treatment of adiponitrile (ADN) with hydrogen in the presence of a nickel-containing catalyst at temperatures not below room temperature and elevated hydrogen partial pressure in the presence or absence of a solvent comprises, after the conversion based on ADN and/or the selectivity based on ACN has or have dropped below a defined value 
     (a) interrupting the treatment of ADN with hydrogen by stopping the feed of ADN and of the solvent, if used, 
     (b) treating the catalyst at from 150° to 400° C. with hydrogen using a hydrogen pressure within the range from 0.1 to 30 MPa and a treatment time within the range from 2 to 48 h, and 
     (c) then continuing the hydrogenation of ADN with the treated catalyst of stage (b).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improved process for thecoproduction of 6-aminocapronitrile (ACN) and hexamethylenediamine (HMD)by treatment of adiponitrile (ADN) with hydrogen in the presence of anickel-containing catalyst at temperatures not below room temperatureand elevated hydrogen partial pressure in the presence or absence of asolvent.

The present invention further relates to a process wherein the treatmentof ADN is carried out in suspension or in a fixed bed in a downflow oroutflow process.

2. Description of the Related Art

The hydrogenation of ADN to 6-aminocapronitrile in the presence ofsolvents, especially ammonia, and nickel-containing catalysts has beendescribed in detail for example in U.S. Pat. No. 2,762,835, U.S. Pat.No. 2,208,598 and WO 92/21650.

The nickel-containing catalysts used in the hydrogenation of ADN loseactivity in long runs and therefore have to be replaced with newcatalysts once the activity has dropped below a certain value.

Nickel-containing catalysts are widely used in industry for steamreforming, for methanization and for the hydrogenation of functionalgroups such as CO double bonds, C--C multiple bonds or nitrile groups.In many of the aforementioned applications the catalyst is deactivatedsooner or later through the formation of carbonaceous deposits on theactive catalyst surface. The formation of carbonaceous deposits in steamreforming and the removal of these layers by reaction with oxygen,hydrogen, steam or carbon dioxide is described in Trimm, Catal. Rev.Sci.Eng., 16(2), 155-187 (1977). Measurable reaction rates are achieved withhydrogen only at temperatures above 550° C.

The regeneration of catalysts coated with carbonaceous deposits isgenerally effected by burning off the organic coatings with nitrogen-airmixtures. However, this method can be used only with catalysts whichremain stable on reaction with air supported catalysts with a stablestructure of oxidic material, such as SiO₂, Al₂ O₃, TiO₂, can besuccessfully regenerated by this method. For instance, GB-A 2,284,163describes the regeneration of a supported catalyst with Pt, Pd, Ru, Rh,etc. or nickel by treatment of a gas containing at least chlorine andoxygen.

Catalysts with very high metal contents become damaged on burning offthe organic deposits with air, altering their mechanical properties (seeEP-A 61,042).

EP-A 61,042 also discloses that nickel-containing catalysts having amaximum nickel content of 50% by weight for the hydrogenation ofbutynediol to butanediol can be regenerated by hydrogen treatment attemperatures between 200° and 500° C., preferably at temperatures above275° C.

Similarly, U.S. Pat. No. 5,310,713 describes a regeneration withhydrogen for an alkylation catalyst which may contain nickel, but theregeneration with hydrogen is carried out in the presence of liquidalkane and of a chloride source.

It is known from Journal of Catalysis 143 (1993), 187-200, that a nickelcatalyst (25% by weight of Ni on SiO₂) which is used for thehydrogenation of acetonitrile in the gas phase can be regenerated bytreatment with hydrogen at temperatures of above 200° C.

The cited references do not reveal whether it is also possible toregenerate nickel-containing catalysts used in the hydrogenation ofhigher boiling dinitriles, especially adiponitrile. For bifunctionalcompounds such as dinitriles, in particular, can give rise, underreaction conditions, to the formation of oligomers which lead toregeneration problems.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process whereby itis possible to regenerate the nickel-containing catalysts used inhydrogenation of ADN to ACN and HMD in a simple way, without incurringlong shutdown times during the regeneration of the catalysts. Moreparticularly, the object is to raise catalyst activity in respect ofconversion and selectivity in the hydrogenation of ADN as closely aspossible to the level of the unused catalyst.

We have found that these objects are achieved by a process for thecoproduction of 6-aminocapronitrile (ACN) and hexamethylenediamine (HMD)by treatment of adiponitrile (ADN) with hydrogen in the presence of anickel-containing catalyst at temperatures not below room temperatureand elevated hydrogen partial pressure in the presence or absence of asolvents which comprises, after the conversion based on ADN and/or theselectivity based on ACN has or have dropped below a defined value

(a) interrupting the treatment of ADN with hydrogen by stopping the feedof ADN and of the solvent, if used,

(b) treating the catalyst at from 150° to 400° C. with hydrogen using ahydrogen pressure within the range from 0.1 to 30 MPa and a treatmenttime within the range from 2 to 48 h, and

(c) then continuing the hydrogenation of ADN with the treated catalystof stage (b).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The nickel catalysts used can be customary Raney nickel catalysts (asfixed-bed or suspension catalysts) or supported catalysts. Raney nickelcatalysts are known and commercially available or preparable in a knownmanner from a nickel-aluminum alloy by treatment with a base such assodium hydroxide solution. The support used may typically be alumina,silica, activated carbons, titania and zirconia. Supported catalystscustomarily have a nickel content within the range from 3 to 95,preferably 20 to 95, especially from 50 to 95, % by weight, based on thetotal mass of nickel and support.

The catalysts may also be modified, if desired, with metals of group VIB(Cr, Mo, W) and VIII of the periodic table (Fe, Ru, Os, Co, Rh, Ir, Pd,Pt) and also with copper, rhenium or manganese, in which case the nickelcontent of the catalyst is generally within the range from 50 to 99.9,preferably from 80 to 99, % by weight, based on the active components(nickel+modifier).

Furthermore, the catalysts may be modified with a compound based on analkali metal or an alkaline earth metal such as lithium, sodium,potassium, rubidium, cesium, magnesium, calcium, strontium and barium,especially cesium. It is customary to use a weight ratio within therange from 0 to 5, preferably from 0.1 to 3, % by weight of alkali metalor alkaline earth metal to nickel.

The nickel catalysts usable according to the invention may be preparedin various ways. The preparation of supported nickel catalysts iscustomarily effected by impregnating a ceramic support with an aqueousorganic solution of a nickel salt and, if desired, the modifier, thendrying and calcining in a conventional manner. The solubility of thesalts and pore volume of the support limits, according to observationsto date, the amount of nickel which can be applied by one impregnatingstep, so that, if desired, the impregnating procedure may have to berepeated more than once, in which case, in general, the catalyst isdried and calcined after each impregnating step in order that thedesired level of nickel may be obtained on the catalyst. It is alsopossible to apply nickel by precipitation of a sparingly soluble nickelcompound such as the corresponding hydroxide or carbonate compound to asupport suspended in the precipitation solution. The precipitates can beshaped in a conventional manner, customarily after filtration or spraydrying.

The hydrogenations can be carried out with preference in upflow,downflow or suspension processes.

When the reaction is carried out in a suspension, it is customary tochoose temperatures within the range from 40° to 150° C., preferablywithin the range from 50° to 10° C., particularly preferably within therange from 60° to 90° C.; the pressure is generally chosen to be withinthe range from 2 to 20, preferably 3 to 10, particularly preferably from4 to 9, MPa. The residence times are essentially dependent on thedesired yield, selectivity and the desired conversion; customarily, theresidence time is selected so as to maximize the yield, for examplewithin the range from 50 to 275, preferably within the range from 70 to200, min.

In the suspension process, the solvent used is preferably ammonia,amines, diamines and triamines having from 1 to 6 carbon atoms such astrimethylamine, triethylamine, tripropylamine and tributylamine oralcohols, especially methanol and ethanol, particularly preferablyammonia. It is advantageous to use a dinitrile concentration within therange from 10 to 90, preferably from 30 to 80, particularly preferablyfrom 40 to 70, % by weight, based on the sum of dinitrile and solvent.

The amount of catalyst used is generally within the range from 1 to 50,preferably from 5 to 20, % by weight, based on the amount of dinitrileused.

The suspension hydrogenation can be carried out batchwise or,preferably, continuously, generally in the liquid phase.

The hydrogenation may also be carried out batchwise or continuously in adownflow or upflow process in a fixed-bed reactor, in which case it iscustomary to employ a temperature within the range from 20° to 150° C.,preferably within the range from 30° to 90° C., and a pressure generallywithin the range from 2 to 30, preferably within the range from. 3 to20, MPa. The hydrogenation is preferably carried out in the presence ofa solvent, preferably ammonia, amines, diamines and triamines havingfrom 1 to 6 carbon atoms such as trimethylamine, triethylamine,tripropylamine and tributylamine or alcohol, preferably methanol andethanol, particularly preferably ammonia. In a preferred embodiment, theamount of ammonia used is within the range from 0.5 to 10, preferablyfrom 1 to 6, g per g of adiponitrile. Preference is given to using acatalyst space velocity within the range from 0.1 to 2.0, preferablyfrom 0.3 to 1.0, kg of adiponitrile/l*h. Here too it is possible toadjust the conversion and hence the selectivity in a specific manner byvarying the residence time.

The hydrogenation can be carried out in a customary suitable reactor.

If the reaction is carried out in the gas phase, it is customary to usetemperatures within the range from 100° to 250° C., preferably withinthe range from 160° to 200° C.; the pressure employed is generallywithin the range from 0.01 to 3, preferably from 0.09 to 0.5, MPa.Furthermore, the molar ratio of hydrogen to ADN is generally within therange from 2:1 to 300:1, preferably within the range from 10:1 to 200:1.

In a preferred embodiment, the hydrogenation of ADN is carried out inthe presence of ammonia as solvent using fixed-bed catalysts asdescribed above by a process wherein, following the deactivation of thecatalyst, ie. a decrease in the conversion of ADN and/or selectivitybased on ACN below a defined value, first the feed of adiponitrile andammonia is switched off, then the temperature is brought to 200°-250°C., and subsequently the catalyst is treated for from five to six hourswith from 200 to 800, preferably from 500 to 700, especially 600, l ofhydrogen/l of cat.×h. Thereafter the temperature is customarily broughtback down to reaction temperature and the hydrogenation is continued.

Prior to starting the regeneration, it is preferable to remove thehydrogenation mixture still present in the reactor. It may further beadvantageous, especially if the treatment of the ADN with hydrogen iscarried out in suspension, to wash the catalyst before the actualregeneration, ie. after interruption of the treatment of ADN withhydrogen (stage (a)) and before treatment with hydrogen (stage (b)),with the solvent present in the system, especially with liquid ammonia.The wash temperature employed is customarily within the range from 20°to 200° C., especially within the range from 20° to 100° C. It isgenerally advantageous to carry on the wash for a period of from 2 to 24hours.

From experience to date, the regeneration can be carried out at anydesired time. From an economic point of view, a regeneration appears tobe sensible when the conversion based on ADN and/or the selectivitybased on ACN has dropped by more than 10%, based on the initial value.

According to the invention, the regeneration of the catalyst is carriedout at temperatures within the range from 150° to 400° C., preferablywithin the range from 180° to 270° C., especially within the range from200° to 250° C., using a hydrogen pressure within the range from 0.1 to30 MPa, preferably within the range from 0,1 to 20 MPa, and a treatmenttime within the range from 2 to 48 h, preferably within the range from 2to 24 h. A continuous process is customarily carried out with thehydrogen rate within the range from 100 to 1500, preferably within therange from 200 to 1000, l of hydrogen/l of reactor volume×hour.

The process of the invention makes it possible to achieve distinctimprovements in the life and space-time yield of nickel catalysts in thehydrogenation of adiponitrile to 6-aminocapronitrile andhexamethylenediamine (nylon 6 and nylon 66 intermediates).

EXAMPLES Example 1

(Suspension Hydrogenation)

Reactor: 250 ml autoclave with sampling port (material of construction:HC 4); agitation by disk stirrer.

Batch: in each case 48 g of ADN, 5.6 g of Raney nickel (BASF, H 1-50,water-moist).

Raney nickel was introduced into an autoclave under a protective gas(argon). The autoclave was then sealed and 150 ml of liquid NH₃ wereinjected. After brief stirring, the bulk of the ammonia was pressed outof the reactor via a riser pipe equipped with a frit. This process wasrepeated six times with 50 ml of liquid ammonia each time to obtainanhydrous Raney nickel as a representative starter catalyst (ammoniaholdup about 100 ml). Thereafter the system was heated to 80° C., 48 gof adiponitrile were metered in, and the pressure was raised withhydrogen to 7 MPa. Catalyst-free samples of the liquid phase wereremoved through the sampling port after 20, 45, 90, 135, 180 and 225min.

After 225 min, the temperature in the reactor was reduced to 25° C. andthe catalyst-free reaction mixture was removed. The catalyst remainingin the reactor was rinsed six times with 50 ml of liquid ammonia eachtime, at room temperature, by the method described for the wash prior tothe first use. For the subsequent run the system was heated back up to80° C. and the reactants were metered in afresh. The runs with samplingand washing were repeated a number of times.

Table 1 shows the conversion of the adiponitrile and the selectivity to6-aminocapronitrile as evident from the GC data after a hydrogenationtime of 225 min. Apart from ACN, hexamethylenediamine was formed almostexclusively.

                  TABLE 1                                                         ______________________________________                                        Run         ADN conversion                                                                            ACN selectivity                                       ______________________________________                                        1           84.2        59.6                                                  2           49.6        70.4                                                  3           43.4        64.7                                                  4           37.3        70.1                                                  5           30.6        75.2                                                  6           29.2        75.2                                                  7           26.3        77.2                                                  8           24.2        80.0                                                  9           17.3        79.5                                                  10          16.2        85.0                                                  11          13.2        81.6                                                  12          9.0         86.8                                                  13          7.4         95.3                                                  14          6.0         85.5                                                  15          5.3         84.6                                                  16          5.4         87.2                                                  17          4.9         90.3                                                  18          5.8         88.2                                                  ______________________________________                                    

Following run 18, the hydrogenation mixture was removed and thedeactivated catalyst was rinsed six times with liquid ammonia.Thereafter the ammonia was completely decompressed and entirelydisplaced from the reactor using argon. The reactor was then heated to100° C. and once more flushed with argon. The argon was then displacedby flushing with hydrogen. The reactor was then heated to 250° C. andthe pressure set with hydrogen to 10 MPa. The reactor was left at 250°C. for 5 hours. The autoclave was then heated down to room temperature,the gas-phase was completely decompressed, and the next block of runswas started.

                  TABLE 2                                                         ______________________________________                                        Run after regeneration of catalyst                                            Run         ADN conversion                                                                            ACN selectivity                                       ______________________________________                                        19          54.9        80.5                                                  ______________________________________                                    

Regeneration with hydrogen made it possible to raise the conversionbased on ADN from 5.8% to 54.9%.

Example 2

(Continuous Gas Phase Hydrogenation)

Catalyst Preparation

4 mm Al₂ O₃ extrudates (SPH 512 B, Rhone Poulenc) were initiallyimpregnated for two hours at room temperature with an aqueous, 3.5%strength by weight CsNO₃ solution, then air-dried at 120° C. for 16 hand subsequently calcined in air at 350° C. over 4 h. The extrudatesthus calcined were then impregnated with an aqueous, 44.3% strength byweight Ni(NO₃)₂ solution for 2 h, then air-dried at 120° C. for 16 h andsubsequently calcined in air at 350° C. over 4 h. Thereafter theimpregnation, drying and calcining was repeated with the nickel saltsolution.

After cooling, the extrudates were installed in a reduction apparatusand flushed for 2 h at room temperature with 20 l/h of N₂ to remove air.This was followed by heating to 300° C. with a heating rate of 2° C./minand a hydrogen flow of 20 l/h of H₂ and the 300° C. were maintained for2 h.

The catalyst thus prepared contained 0.1% by weight of Cs and 13% byweight of Ni, based on the total weight of the extrudates.

Hydrogenation

40 g/h of adiponitrile were introduced into a vaporizer (280° C.) andpassed from there with 400 /h of hydrogen through a tubular reactor(packed with 330 g of catalyst; reactor dimensions: length=2000 mm,diameter=15 mm) in the downflow direction. The reactor temperature was180° C. The gaseous reactor effluent was condensed in cold traps andanalyzed by gas chromatography. Following a startup phase, theadiponitrile conversion obtained was 45.2%, which dropped to 24.1% overa period of 445 h. The aminocapronitrile selectivity was within therange from 80 to 90%.

The dinitrile feed was then turned off and the catalyst regenerated inthe reactor with 200 l/h of hydrogen at 250° C. over 6 hours. Followingrenewed startup under identical conditions (see above), a conversion of42.7% was obtained; that is, the catalyst had almost been restored toits initial activity.

Example 3

(Fixed-Bed Hydrogenation in the Liquid Phase)

Catalyst Preparation

2.5 kg of an NiAl alloy (from BASF, H1-55) were impregnated at 80° C.with stearic acid. After comminution of the cooled and solidified mass,the powder obtained was pressed into tablets (3 mm height, 3 mmdiameter). The tablets thus obtained were then calcined at 900° C. over2 h. The activation of the tablets was carried out with sodium hydroxidesolution. For this, 2.4 kg of the tablets were introduced into 5.7 l ofwater and then admixed with vigorous stirring to a total of 1.44 kg ofNaOH platelets. On completion of the addition the stirring was continuedat 90° C. for a further 24 h. After cooling, the activated tablets werewashed with water until the wash liquor was pH-neutral.

The activated catalyst tablets were installed in the reactor under waterand rinsed with ammonia.

Hydrogenation

370 g/h of adiponitrile and 1.1 kg/h of ammonia were passed with 500 l/hof hydrogen through a tubular reactor (packed with 740 ml of catalyst;length=1800 mm, diameter 30 mm) in the upflow direction. The reactortemperature was 50° C., the pressure was 20 MPa. The reactor effluentwas analyzed by gas chromatography. Following a startup phase anadiponitrile conversion of 45% was obtained, which dropped to 20% over aperiod of 280 hours. The aminocapronitrile selectivity rose frominitially 80 to 90%.

The dinitrile and ammonia feed were then switched off and the catalystregenerated in the reactor at 200° C. and a hydrogen pressure of 20 MPa(at 500 l/h of hydrogen) for 5 hours. After renewed startup underidentical conditions (see above) the conversion rose to 45% (at an ACNselectivity of 80%); that is, the catalyst had been restored to itsinitial activity.

We claim:
 1. In a process for the coproduction of 6-aminocapronitrile(ACN) and hexamethylenediamine (HMD) by the hydrogenation ofadiponitrile (ADN) to convert ADN to both ACN and HMD, saidhydrogenation taking place at a temperature of from 40° to 150° C. at ahydrogen partial pressure of from 2 to 20 MPa in the optional presenceof a solvent or the hydrogenation takes place in a fixed bed reactor ina downflow or upflow process at from 20° to 150° C. and at a pressure offrom 2 to 30 MPa, the improvement which comprises: continuing theconversion of ADN to ACN and HMD until the conversion of ADN has droppedbelow a pre-determined value or until the selective conversion to ACNhas dropped below a pre-determined value, and thereafter(a) interruptingthe hydrogenation of ADN by stopping the feed of ADN and of the solvent,if used, (b) treating the catalyst at from 150° to 400° C. with hydrogenusing a hydrogen pressure within the range from 0.1 to 30 MPa and atreatment time within the range from 2 to 48 h, and (c) then continuingthe hydrogenation of ADN with the treated catalyst of stage (b).
 2. Theprocess of claim 1, wherein the treatment of ADN with hydrogen iscarried out in suspension at a temperature within the range from 50° to100° C. and a pressure within the range from 3 to 10 MPa.
 3. The processof claim 1, wherein the treatment of ADN with hydrogen is carried out ina fixed-bed reactor in a downflow or upflow process at a temperaturewithin the range from 20° to 150° C. and a pressure within the rangefrom 2 to 30 MPa.
 4. The process of claim 2, wherein, followinginterruption of the treatment of ADN with hydrogen (stage (a)) andbefore the treatment of the catalyst with hydrogen (stage (b)), thecatalyst is rinsed with liquid ammonia and, after the rinse, the ammoniais displaced with an inert gas.